(1) What is the maximum memory for 32 bit Linux?
Normally, Linux split 4G address space into two parts: 3G for user space virtual address and 1G for kernel virtual address.Here are some solutions:
a). HIGHMEM solution for up to 4G
Use the kmap to map the memory in ZONE_HIGHMEM to ZONE_NORMAL
b). HIGHMEM solution for using 64G memroy (36bit bus address)
This is enabled via PAE(Physical Address Extension) extension of the Pentiumpro processor. Then map ZONE_HIGHMEM to ZONE_NORMAL
(2) What is the maximum memory for 64 bit linux?
Based on this, it is 16T, which is controlled by:
arch/x86/include/asm/sparsemem.h:
# define MAX_PHYSMEM_BITS 44
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